Physiological and Perceptual Responses to Exercise according to the Locus of Symptom Limitation in People with COPD

• Main Author: Tracey, Lauren
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Chronic obstructive pulmonary disease; Dyspnea; Exercise; Kinesiology; Physiology; Respiration; Ventilation
• ISBN: 9798708701268

Exercise intolerance is pervasive in people with mild-to-very severe chronic obstructive pulmonary disease (COPD) and is associated with adverse health outcomes, including premature death. The mechanisms of exercise intolerance in COPD are complex and multifactorial but include pathophysiological abnormalities in pulmonary mechanics and limb muscle function. It follows that the exercise tolerance of people with COPD is often limited by intolerable 'and/or leg discomfort. The objective of this study was to compare detailed physiological and perceptual parameters at the symptom-limited peak of incremental cardiopulmonary cycle exercise testing in adults with COPD reporting '(B), leg discomfort (LD), or a combination of 'and leg discomfort (BOTH) as their main exercise-limiting symptom(s). Based on our understanding of pathophysiological mechanisms of exertional 'in COPD, we hypothesized that people stopping exercise because of 'would have relatively greater abnormalities in breathing mechanics than people stopping exercise because of leg discomfort alone or in combination with breathlessness. In this retrospective study, we compared physiological and perceptual responses at the symptom-limited peak of incremental (5-10 W/min) cardiopulmonary cycle exercise testing between 35 people with COPD reporting B (26M; mean +/- SD FEV1, 52 +/- 24%pred), 42 people reporting BOTH (19M; FEV1, 54 +/- 19%pred) and 16 people reporting LD (15M; FEV1, 67 +/- 20%pred) as their main exercise-limiting symptom. Despite similarly impaired levels of baseline lung function, health status, symptomology and exercise capacity, people with COPD whose primary limitation to exercise was B presented with evidence of greater dynamic lung hyperinflation and more severe restrictive constraints on tidal volume (VT) expansion at end-exercise than people whose primary or co-primary exercise-limiting symptom was LD. To this end, both the decrease in inspiratory capacity (∆IC) from rest to peak exercise (p=0.054) and the VT-to-IC ratio at end-exercise (p=0.001) were higher in B vs. BOTH and LD. Furthermore, a higher proportion of subjects in B vs. BOTH and LD had a ∆IC of 400 mL or greater (p=0.073) and a peak VT%IC of 73% or greater (p<0.001), respectfully reflecting severe dynamic lung hyperinflation and severe restrictive constraints on VT expansion during exercise. These findings were further validated by the higher frequency of responses in B vs. BOTH and LD of qualitative descriptors of breathlessness at end-exercise, particularly those relating to 'unsatisfied respiration' (p<0.05), 'air hunger' (p<0.05), and 'suffocation' (p<0.05). The results of this study support the hypothesis that the locus of symptom limitation reflects the proximate pathophysiological source of exercise intolerance in people with COPD. Once prospectively validated, our findings may lead to more personalized and effective clinical management of exercise intolerance in symptomatic adults with COPD.